What is the origin of the legend of the old tomb in Gujingguan Xishan?

It came from ancient times and sealed the ancient coffin. Introduction to the legend of Gujingguan: The whole world only knows that there is Quanzhen religion in Zhong Nanshan, but it doesn't know that there is a dilapidated Taoist temple under Zhong Nanshan. The world only knows that Maoshan is good at catching ghosts, sharp and evil, and Yang Gui knows Feng Shui, but he doesn't know the most about Heaven. On that day, the man in Gujingguan was born and became famous all over the world.